This invention generally relates to cathode ray tubes and, more particularly, to a tension mask having a frequency distribution with improved vibration damping.
A color picture tube includes an electron gun for forming and directing three electron beams to a screen of the tube. The screen is located on the inner surface of the faceplate of the tube and comprises an array of elements of three different color emitting phosphors. An aperture mask is interposed between the gun and the screen to permit each electron beam to strike only the phosphor elements associated with that beam. The aperture mask is a thin sheet of metal, such as steel, that is contoured to somewhat parallel the inner surface of the tube faceplate. An aperture mask may be either formed or tensioned.
The aperture mask is subject to vibration from external sources (e.g., speakers near the tube). Such vibration varies the positioning of the apertures through which the electron beams pass, resulting in visible display fluctuations. Ideally, these vibrations need to be eliminated or, at least, mitigated to produce a commercially viable television picture tube.
The present invention provides a tension mask for a cathode-ray tube having a center portion between two edge portions and a parabolic frequency distribution between the edge portions. The center portion has a central frequency distribution value and the edge portions have a relatively lower peripheral frequency distribution value characterized in that the range of variation between the center and edge portions frequency distribution value is in the closed interval of about 8 Hzxe2x89xa6xcex94xe2x89xa612 Hz